Taguchi quality specification categories and the computation of Six-Sigma metrics: analytical and service industry anomalies and their managerial implications
by Eisenhower C. Etienne
International Journal of Six Sigma and Competitive Advantage (IJSSCA), Vol. 6, No. 4, 2011

Abstract: In this paper, we show that the vital Six-Sigma metrics based on traditional Six-Sigma methodology are based on the Taguchi quality specification category defined as 'nominal is best' where defects exist in both tails of the process distribution. We demonstrate that these metrics are significantly in error when applied to the other Taguchi quality specification categories, 'smaller is better' and 'larger is better' that exist in all industries, but which are particularly prevalent in service businesses. Because measurement and the production of accurate process control and improvement metrics are at the core of the Six-Sigma strategy, this anomaly is a potentially very significant one. The results show that, contrary to expectations based on Six-Sigma theory, even high-performance service processes are characterised by low levels of Taguchi robustness. The results also show that service science, in general, and the science of variation, in particular, have the potential to make a significant contribution to the improvement of service quality.

Online publication date: Wed, 15-Jun-2011

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